Rigid foams made from various polymers such as polystyrene, polyethylene, polyurethane, polyvinyl chloride, and the like, have a number of good qualities such as strength, relatively low price, good insulation properties and the like. However, they also have a number of serious shortcomings. For example, some, such as polyurethane foam, are not translucent. Polystyrene foams rapidly yellow upon prolonged exposure to ultraviolet light. Polyester foams are not translucent and must usually be reinforced with some reinforcing component, such as fibreglass. Moreover, polyester foams also turn yellow over time, upon prolonged exposure to ultraviolet light.
Acrylic polymers, such as those made from acrylate and methacrylate monomers, or co-polymers thereof, have an advantage over most polymers because they have a strong resistance to yellowing upon prolonged exposure to ultraviolet light. Foams made from acrylic polymers however, are expensive and difficult to manufacture according to consistent standards. Rigid, clear acrylic foams can be blown with a suitable blowing agent such as a fluorocarbon. An advantage of using a blowing agent such as a fluorocarbon is that the insulation qualities of the acrylic foam can be increased relative to foams which are blown with other non-condensing blowing agents.
Acrylic panels or foams can be used alone or can be sandwiched between panes of glass, or other suitable light transmitting materials, in order to provide attractive roofing, ceiling, wall, partition mediums or decorative panels. Acrylic panels or foams can also be reinforced with minute reinforcing elements such as fibreglass without detracting substantially from the translucency qualities of the panel or foam.
The applicant is aware of the following references which are more or less pertinent to the subject matter of this invention:
______________________________________ U.S. Pat. No. Inventor Issue Date ______________________________________ 3,170,808 Almy et al. Feb. 23, 1965 3,301,930 Boggs Jan. 31, 1967 3,860,371 Willy Jan. 14, 1975 3,959,049 Tanaka et al. May 25, 1976 4,005,958 Porter Feb. 1, 1977 4,419,459 Melchior Dec. 6, 1983 4,530,806 Melchior July 23, 1985 ______________________________________ German Patent Number Owner Issue Date ______________________________________ DE2934352 Sumitomo Mar. 13, 1980 Chemical DE2935484 Mitsui Toatsn Mar. 20, 1980 Chemicals ______________________________________
George E. Murray, the Dow Chemical Company, in a paper entitled "Insulated Daylight Glazing Panels", delivered at the 20th Annual Technical Conference of the Society of Plastics Engineers, Inc., Vol. X, Jan. 27-Jan. 30, 1964, disclosed large celled methyl methacrylate copolymer plastic foam but no details of manufacturing techniques or formulations were given.
U.S. Pat. No. 4,530,806, Melchior, discloses a process of making articles of foamed polymethyl methacrylate comprising a monomeric methyl methacrylate, a plasticizer which in reality is merely another type of methacyrlate, a foaming agent, and a polymerization catalyst. The polymerization step is conducted under pressures in excess of the evaporation pressure of the foaming agent. Subsequently, the polymerized material is subjected to temperatures in excess of the evaporation temperature of the foaming agent, whereby the product is formed.
There does not appear to be any disclosure in Melchior of foaming at ambient pressures or the use of a metal initiator which permits themethacrylate to be polymerized and foamed without the use of pressure for controlling the process. Also, Melchior does not disclose use of a dual mixture feed system whereby catalyst is present in one of the feed mixtures and the metal initiator is present in the other mixture. Further, Melchior does not mention the use of polymer chain length controlling agents to promote short chains in the polymer and consequent cell size, translucency and uniform cell size. Finally, Melchior does not disclose a process of making a methylmethacrylate prepolymer copolymerized with vinyl-monomers, vinyl acetate, or polyvinylchloride.
Boggs demonstrates a process of producing fibre reinforced resin articles whereby a resin coating is applied to a carrier, which in turn is transferred to webs during contact therewith. This process produces a finished product which has a fibre-free surface.
Tanaka discloses a process for the production of artificial leathers whereby polyurethane prepolymer is foamed between a water-vapour permeable substrate, and a release medium. The foam becomes permanently bonded to the water vapour permeable substrate.
German Pat. Nos. DE2934352 and DE2935484 mention the manufacture of glass reinforced panels. They disclose the copolymerization of acrylic monomers and styrene monomers and indicate that this combination changes the refraction index of the resin. These products can purportedly be used with several types of glass fibre to obtain a transparent panel with minimum visibility of the glass fibres.